Carrier Synchronization in a Digital Radio System

Abstract

<p> The problem of coherent carrier recovery and the effects of phase error on the performance of an offset quadrature-phase-shift-keying (QPSK) duobinary system have been investigated in the thesis. The system of interest is similar to RD -3 digital system that is being developed and installed as an efficient high data-rate digital radio communication system by Bell Northern Research Laboratory (BNR). </p> <p> Four carrier regeneration loop structures are investigated and analysed in the thesis. These are: (i) estimate-aided suppressed carrier loop (ii) decision-directed feedback loop (iii) shifted decision-directed feedback loop (iv) half-shifted decision-directed feedback loop All of these loop structures employ the technique of data-aided carrier synchronization. The estimate-aided loop structure exhibits steadystate behavior similar to that of a conventional Costas loop. The remaining three loop structures differ from the estimate-aided loop in the sense that they require decisions to make on the noisy received signal. These are then fedback to the carrier recovery circuit in such a way as to create a spectral line at carrier frequency. The loop behavior in the presence of additive noise has been investigated in some detail. For each loop, analytical expressions for the phase detector characteristic (S-curve) and the steady-state phase error probability density function (pdf) are derived, and provide a means of comparing the performance of the different recovery schemes.</p>